This invention relates to computer-operated printers of the kind that direct a jet of ink onto a passing surface. The invention is mainly intended for use on the kind of ink-jet printer in which the surface to be printed is a small distance away from the ink jet head, i.e the type that is used for printing onto cardboard boxes and the like. In such printers, the (liquid) ink reservoir is in the form of a flexible bag, and the bag is replaceable. The invention is aimed at providing an improved replaceable reservoir.
Previous designs of replaceable reservoirs for ink-jet printers have been based on the principle of sealing the ink in a container and of including a membrane as a portion of the wall of the container. A hollow needle fixed into the printer is arranged to mechanically pierce the membrane when the container, full of ink, is assembled into place in the printer. Ink flows into the printer through the hollow needle, and the membrane material is such as to seal itself around the needle, whereby no ink can leak out.
Both when the full container is assembled to the needle, and when the (nearly) empty container is removed from the needle, the membrane provides an adequate seal around the needle, and the membrane closes itself up, i.e seals itself, after the needle has been removed. The ink reservoir as described herein also is adapted to make use of the needle-and-membrane technology.
Some previous designs of ink reservoirs for ink-jet printers that might be considered relevant to the invention are: U.S. Pat. No. 5,359,356 (Ecklund, October 1994); U.S. Pat. No. 4,183,031 (Kyser, January 1980); and U.S. Pat. No. 4,053,901 (Skafvenstedt, October 1977).
One previous design approach to the replaceable reservoir has been to use a container having fixed or rigid walls. Such containers have been expensive, especially since, as the ink is used, some means of compensating for the reduced volume in the container has to be provided. Movable pistons, which require to be sealed, have added to the complexity and expense. Of course, such systems can be engineered to be leakproof, even if the components are subjected to abusive treatment, but the expense of achieving robust leak-proof reliability has been high.
Another approach has been to provide a flexible bag, which can collapse as the ink is consumed. This addresses the moving-parts problem, but raises the problem of how the bag might be attached to the base component, or plug, in which the membrane is located. The problem of sealing a bag of thin flexible film to a solid, chunky plug, has not previously been resolved adequately, but inexpensive manner. Too often, the joint between bag and plug has been prone to leakage, even when (expensive) care and attention is given especially to the potentially-leaky region of the reservoir during manufacture. Previous designs have included welding, adhesives of various types, and so on, in the attempt to provide a reliable seal.
The invention provides a manner of attaching a bag of flexible plastic film to a chunky, solid plug. Basically, the bag is held tightly between the plug and a tightly fitting ring. The ring holds the film material trapped between itself and the plug. As will be explained, assembly of this manner of attachment, on the production line, is simple enough that even an operator who carries out the assembly with a less than ideal degree of care and attention can readily produce reservoir after reservoir in which the chances of leakage are virtually nil. This level of reliability of the seal is achieved despite the fact that no adhesives or welding are needed.
For an effective seal, the ring should grip the film of the bag very tightly around the plug. The designer should see to it that the ring is of such dimensions as to support the stresses induced by the tight fit. The designer should have it in mind that plastic materials tend to settle or creep over a period of time, to a new dimension in which the stress is reduced. Thus, even though a badly-designed ring might produce a tight fit at first, such a ring might gradually xe2x80x9cgivexe2x80x9d slightly, and the tight fit would be relaxed. The stresses induced in the ring must be kept low enough that the tight fit can be maintained indefinitely. Therefore, the ring and the plug should be thick and chunky.
It is recognised that a plug and a ring of such suitable dimensions as to hold the tight fit more or less indefinitely can be provided inexpensively, and can be accommodated within the environment available for a replaceable ink-reservoir on an ink-jet printer.
The invention lies in an ink-storage reservoir apparatus for a printer that includes a bag of flexible plastic film. A plug serves to close a mouth of the bag, and thereby to define an ink container in the bag. The plug has an outward-facing surface, and the mouth of the bag is placed thereover, and the surface of the plug is so dimensioned, in relation to the mouth of the bag, as to cause the material of the mouth of the bag to stretch over the plug. The apparatus includes a ring, and the ring has an inward-facing surface, which is complementary to the outward-facing surface of the plug. The ring is a tight interference fit over the material of the mouth of the bag when the mouth of the bag is stretched over the outer surface of the plug. The ring is pressed over the plug and encircles the plug, and serves to grip the material of the mouth of the bag, tightly and securely, between the outward-facing surface of the plug and the inward-facing surface of the ring.